Control system for rolling mills



G. E. sToL-rz L CONTROL SYSTEM FOR ROLLING MILLS April 28,1942.

@Lawn p Bm xOhuN k.

Filed April 28, 1938 4 Sheets- Sheet l Wk hk.

oli

PQ mm. 4 NN AQ.

IIIINI aus ` INVENTOR G/e'nn 5570/22- M ATTO EY mmm.

NNW

VgNESS-IS: ZMMW .April 28, 1942. G45. sToL-rz 2,281,083

CONTROL SYSTEM FOR ROLLING MILLs Filed April 28, 1958 4 Sheets-Sheet 2 April 28, 1942. G, E, sTQL-rz 2,281,083

CONTROL SYSTEM FOR ROLLING MILLS Filed April 28, 1938 4 Sheets-Sheet 5 INVENTOR 5% Z G/enn 5570/72.

ATTORN Y April 28, 1942. G, E, sToL-rz 2,281,083

CONTROL SYSTEM FOR ROLLING MILLS Filed April 28, 1938 4 Sheets-Sheet 4 WITNESSESI INVENTOR l /nn .o/z.

Patented Apr. 28, 1942 4,

CONTROL SYSTEM FOR ROLLING MILLS Glenn E. Stoltz, Edgewood, Pa., assigner to Westlnglxouse Electric & Manufacturing Company, mEastPittsburgh, Pa., a corporation of Pennsyl- Application April 28, 1938, Serial No. 204,711

z claims.

My invention relates, generally, to control systems and, more particularly, to control systems for single stand or tandem mills for rolling metallic strip.

In the operation of tandem mills for rolling strip material, devices have been provided for tensioning the strip material vas it passes through the rolls. This tensioning of the material results in a greater reduction of the strip per roll stand so that fewer roll stands are necessary for a given amount of reduction in strip thickness than would be necessary if such tension were not provided. A further advantage of tensioning the material between the rolls is that the material is held firmly in position during the rolling process.

Higher rolling speeds are sometimes also possible when this tensioning is used and the physical properties of the steel so produced may be improved.

The patent to W. G. Cook, No. 1,982,338, dated November 27, 1934, discloses a system for maintaining a predetermined tension on strip mate rial between a reel from which' the material is being unwound and the reducing roll which is operating on the material. The application of G. P. Lessmann, Serial No. 133,419, filed March 27, 193'?, now Patent No. 2,189,609, issued February 6, 1940, discloses a system for maintaining a predetermined tension on a strip of material as it passes between two adjacent roll stands of a tandem mill. This provides front tension on the strip leaving the preceding roll stand and back tension on the strip entering the succeeding roll stand.

It will be seen that where tension on the strip material is provided by a device that bears on the strip as it passes between adjacent roll stands, Y

a length of the leading end of the strip will be rolled without front tension as it is being threaded through jthe mill since such tensioning devices cannot operate to tension the strip until the strip is engaged by the rolls preceding and succeeding the tensioning device. In a like manner the winding reel cannot provide forward tension on the strip until the strip has passed from the last roll stand to the winding reel.

The same situation exists when the following end of the strip is passed between the unwinding reel and the iirst roll stand as back tension cannot be applied to the strip by the unwinding reel after it has left the unwinding.reel. Likewise, back tension cannot be applied to the strip between adjacent roll stands while the following'end is passing between the roll stands.

As a result of the failure to provide both front and back tensions on the ends of the strip, the ends are thicker than the rest ofl the strip since they are not reduced as much as that part of -the strip which has received the proper front and `back tensions while passing through the rolls.

It has been found in the operation of hot strip rolling mills that there is such a temperature gradient along the strip as it passes through the mill as to so aiect the resistance-to-reduction of the strip as to result in increased thickness oi.' rolled strip toward the following end of the strip.

These variations in thickness of the rolled material due both to lack of proper tensioning of the strip and to cooling of the strip make it necessary to sort the sheets cut from the finished strip, so thatI the gauge of the material may be kept within the tolerances permitted by the customers specifications. If these variations are too great, it is necessary to scrap some of the material. Both scrapping of material Aand the process of sorting the finished material add considerably to the cost of production.

An object of this invention is to provide a control system for a single stand or a tandem mill for rolling strip or other rolled products such as rod wire or any sectional material where tension is applied to the material las it is being rolled, which shall function to produce a` product of more uniform thickness and of predetermined physical characteristics.

A further object of the invention is to provide a controlv system' for a tandem mill for rolling strip material which shall function to so adjust the tension on the strip of material between the roll stands and the Winding land unwinding reels and between adjacent roll stands as to produce predetermined reducing forces upon the strip of material throughout the entire length of the strip as it passes through the mill.

A further object of my invention is to provide a control system for a single stand or tandem mill for rolling strip material which shall function to vary the roll spacing by screw down control in response to variations in temperature and/or thickness of the strip.

Another object of the invention is to provide a control system for a single stand or tandem mill for-rolling strip material which shall function to vary the tension on the strip of material as it passes through the mill in response to variations of the temperature and thickness of the strip.

These and other objects and advantages of the invention will be apparent from the following detailed description taken in connection with the one embodiment of my invention applied thereto showing the cooperative relationships of the invention with the rolling mill and,

Fig. 4 which is a diagrammatic View of a modication of the thickness and temperature responsive means for controlling the reducing forces on the strip. Fig. 4 includes most of the structure shown in Fig. 3 and is so drawn as to permit it to be substituted for Fig. 3 in the group of gures consisting of Figs. 1, 2 and 3, the system being complete and operative with the apparatus of either Fig. 3 or Fig. 4 used in connection with the apparatus of Figs. 1 and 2.

In carrying out my invention I provide means for causing the unwinding reel motor of a strip rolling mill to act as a braking generator to provide an abnormal back tension on a strip as the end of the strip passesv between the first two roll stands. When the end of the strip is engaged by the rolls of the second roll stand a corrective abnormal tension is applied to the strip between the rst and second roll stands and the back tension applied by the unwinding reel motor is reduced to a value below normal.

As the end of the strip progresses through the mill the tensions on the material are so adjusted f by varying-thev tensions between adjacent roll stands and between the end roll stands and the reels as to provide an abnormal tension on the material at each roll stand as the leading end is threaded through the mill.

After the leading end is started on the windingreel the tensions between each pair of adjacent roll stands and between the end roll stands and the 4reels is automatically adjusted to a predetermined manually adjustable normal amount for each position. When the following end of the strip leaves the unwinding reel the tensions between the roll stands and between the winding reel and the last roll stand are varied to produce predetermined abnormal tensions on the material at each roll stand until the end leaves the last roll stand. f

Temperature responsive means and thickness responsive means areY provided for varying the strip tension in accordance with variations of strip temperature and gauge to compensate for the cooling of the strip when the system is 'used to control a hot strip mill-and to compensate for varying physical characteristics ofthe strip material. Thickness responsive means arc provided to correct varying thickness in metal coming to the mill as'it is rolled.

Referring now to the drawings:

I have shown a four-stand strip rolling mill having roll stands L, M,.N and O with the strip of material 4Il) being unwound from the unwinding reel R passing through the rolls ofthe fourroll stands and being wound on the winding reel S. The rolls of roll stands L, M, N and O are driven by motors I2, I4, I 6 and I 8, respectively, and the Winding and unwinding reels are driven by motors 20 and 22, respectively. A vibrating regulator G is connected in the eld circuit of the reel motor 22 and is controlled by the armature current of the motor 22 to regulate the back tension applied to the strip l0.

Tension is applied to the strip I0 as it passes betweenadjacent roll stands by tensioning devices H, I and J which bear upon the strip between the stands L and M, M and N, and N and CII O, respectively.` A vibrating regulator K is provided for so controlling the field current of the winding reel motor 20 as to maintain a constant adjustable tension on the strip as it is Wound upon the reel S.

The vibrating regulator G comprises a vibrating arm 26 upon which are mounted contact elements 28 and 30 which are insulated from the arm. The arm 26 is pivote'd at 32 and is connected to be actuated by the relay 34. The coil of relay 34 is connected in series circuit relation with a resistance element 36 which has such a resistance value as to prevent suflicient current now through relay 34 to cause it to actuate its armature. The contact element 38 of relay 34 is connected inl series circuit relation with the coil of the relay 40. Contact element 42 of relay 40 is connected in shunt relation with resistance element 36. An arm 44 is pivoted at 48 and is connected to be actuated by the armature of solenoid 58. Contact element 52- is mounted upon arm 44 and electrically connected therewith and is disposed. between contact elements 28 and 30. The coil of solenoid 50 is connected in parallel circuit relation with the series field winding 54 of the reel motor 22 in series circuit relation with the resistance elements G3 and G4.

The movable contact elements 28 and 30 of the regulator are connected in circuit with the coils of relays 56 and 58, respectively. The resistance elements 60 and 62 are connected in series circuit relation with the shunt eld winding 64 of reel motor 22 and with resistance elements GI and G2. The contact element 66 of relay 56 is connected in shunt relation with resistance element 60 and the contact element 68 of relay 58 is connected in shunt relation with the resistance element -62- when relay 58 is energized.

It will be seen that the arm 26 will be caused to vibrate continuously because of the intermittent energization of the coil of solenoid 34. When the coil of solenoid 34 is energized, contact element 38 will be closed to energize the coil of relay 40 which in turn moves its contact element 42 to the open circuit position to connect the resistance element 36 in series circuit relation with solenoid 34 to thus cause it to drop its armature. The dropping of the armature of solenoidl 34 will cause Acontact element 38 to move to the open circuit position, thus deenergizing the coil of relay 40 and allowing the contact element 42 to drop to close circuit position, which, in turn, will cause an increase in current flow through the coil of vsolenoid 34 to again cause upward movement of the armature of solenoid 34. The armature of solenoid 50 will occupy a position depending upon the current flow in its actuating coil which, in turn, will depend upon the current flow in the armature of the motor 22. As the arm 26 vibrates contact elements 28 and 38 will intermittently engage contact element 52 and will remain in engagement with contact element 52, and cause energization of the coils of relays 56 and 58 for periods of time during each vibrating movement of the arm 26 depending upon the position in which the contact element 52 is held by arm 44.

It will be seen that if the current in the armature of machine 22' falls below that which is necessary to supply the required torque for the desired back tensioning of the strip- I0 as it is being unwound from reel R, solenoid 50 will allow arm 44 to move downward, and this will permit contact element 52 to remain in contact with contact element 80 tor a longer perlod of time during each vibrating movement of arm 26 than` with contact element 2l. Thus, for each vibrating movement of arm 26 relay I8 will be energized longer than relay 66, and there will be an increase in the current in the shunt neld 04 oi machine 22 because or the decrease in the resistance in the ileld circuit. This increase in iield current will increase the torque of motor 22 to increase the back tension on the strip I0.

The automatic tensioning devices H, I and J are similar and comprise a lever arm 10 on one end of which there is mounted a roller 12 which bears against the strip l0. A iluid pressure piston 14 operating in cylinder 16 is connected to actuate the lever 1l to move the roller 12 into a tensioning position withrespect to the strip I0, the displacement of roller 12 being governed by the iluid pressure in the cylinder 16. The piston 14 and cylinder 16 are so dlmensioned as to permit a leakage from the cylinder chamber to provide a continuous ilow of fluid through the system. This leakage permits escape of pressure fluid, such as air, from the cylinder when it is desired to decrease the pressure in the cylinder, and prevents changes in tension by contraction or expansion of the air in the cylinder, thus providing a constant tension on the strip regardless of the movement of the tensioning roller and the piston. A iiuid pressure reservoir shown is connected through a pressure regulating valve 18 and conduit 80 to the cylinder 16. The pressure regulating valve 18 comprises a valve member 82 and a valve seat 84 cooperating therewith, the valve member 82 being operated by stem 86 which is connected to diaphragm 88 and the core of solenoid 90. Spring members 92 and 94 bear against the diaphragm 88, the spring, member 94 being of such dimensions as to tend to open the valve and to thus increase the pressure in the cylinder 16. The tension of spring 94 is opposed by the pull of the armature of solenoid 90 which pull varies with the current flowing through the coil of solenoid 90, so that the pressure in cylinder 16 and hence the tension applied to strip l by roller 12 will vary inversely with) the current ilowing in the coil of solenoid 90 and the regulator will tend to apply a constant tensioning force to the strip |0 so long as the constant current flows in the solenoid 90. It is to be understood that any suitable pressure regulating valve may be substituted for the valve 18. It is also to be understood that the pressure provided by spring 94 of valve 18 may be provided by an equivalent means such as a Weight or a fluid pressure operated piston.

In order to prevent too great a displacement of the roller 12 as it bears againstl the strip, the regulator H includes a control means for the motor I4 which drives the rolls of roll stand M. This controller comprises contact elements 96 and 98 which are carried by and moved with the arm and therefore change their positions with variations in the position in the arm 10. Con"- tact element 96 is connected in series circuit relation with the coil of relay |00 and contact element 98 is connected in series circuit relation with coil of relay |02. The resistance elements.

|04 and |06 are connected in series circuit relation with the shunt ileld winding |08 of the motor |4 and in the energized position of relay |00 the contact element ||0 thereof is connected in shunt relation with the resistance element |04.

When relay |02 is deenergized its contact element ||2 is connected in shunt relation wlthvthe resistance element |06.

A contact element ||4 is carried by, and electrically connected to an arm III which is pivoted at lll, and the arm |I6 is caused to vibrate by the solenoid |84 under control of relay |40 and resistance element |31 in the manner described in the discussion of the vibration of the arm 26 by the solenoid 84 and the control of relay 4I in connection with the regulator G.

Thus it will be seen that in the event that the arm 10 tends to be displaced too much to maintain a preferred predetermined position, the contact elements 86 and 98 will move to such a position as to cause a longer period oi engagement of contact element ||4 with one or the other of contacts 96 and 98 on each vibrating movement of the arm ||6. This will cause longer energization of one or the other oi relays |00 and |02 and will eiect a change in the current flow in the field winding |08 of motor I4 which will tend to decrease or increase the speed of the motor.

In this manner the tension roller 12 will be reciated motors.

the strip I0, the current flowing in the coil ol.'

solenoid may be decreased by connecting the desired number of resistance elements HI, H2 and H3 in series circuit relation with this coil.

The tensioning reel motor 20 is controlled by regulator K to maintain an adjustable constant tension on vthe strip I0 as it is delivered from the last roll stand O. The regulator K comprises substantiallyl the same elements as described hereinbefore in the discussion of the regulator G for the unwinding reel motor 22, except that in this instance the regulator K is connected to cause aI decrease in the energization of the shunt eld Winding'l20 of winding reel motor 20 in response to a decrease in the armature current of motor 20 to thus cause the motor 20 to tend to increase itsl speed and to thus increase the tension on the strip |0. The motor 20 is controlled to maintain the desired tensions on the strip |0 by connecting the desired number of resistances KI, K2 in series circuit relation with the field winding |20 of the motor 20 to control its shunt iield current. The regulator K may be adjusted to maintain the selected tensions on the strip I0 by connecting the desired number of resistance elements K3, K4 in series circuit relation with the coil of its operating solenoid |22.

Relays A, B, C, D, E and F are connected in parallel circuit arrangement with the series eld windings of motors 22, I2, I4, |6, I8 and 20, respectively, and are so designed as to be actuated when a load is carried by their respective asso- The relays A, B, C, D, E and F have the series of contacts shown which are connected in circuit to govern the tensions applied by the tensioning devices H, I and J, the back tension applied by the reel R and the front tension applied by the reel S. The detailed circuits governed by these relay contact elements will be described hereinafter.

The energization of motor 22 is controlled by a circuit breaker |26 which, when energized, connects motor 22 to the source of direct current power as `shown. 'Ihe operating coil of circuit breaker |26 is connected in circuit through the contact element of a manually operated push button switch |28. A holding circuit is provided for the operating coil of circuit breaker |26 comprising the contact element |30 of relay |32, the

contact element |30 closing a circuit in parallel circuit relation with the contact element of the push button switch |20. The coil of relay |32 is energized from the source of power for motor 22 and the contact element |30 is held in closed circuit position while the motor 22 is energized.

The motor 20 is connected to the source of direct current power by circuit breaker |34 which may be energized by the manually controlled circuit breaker' |36 and which may also be energized by the manually controlled circuitv breaker |38 through a circuit which includes the contact element E of relay E. The contact element l|4| controls a holding circuit for the coil of.circuit breaker |34, this holding circuit comprising a circuit in parallel circuit relation with the manually controlled circuit breaker |38.

In the operation of the system, the leading end of the strip I0 is unwound from the'unwinding reel R and fed toward the iirst roll stand L when the motor 22 is started by momentarily closing the manually controlled push button switch |20. When motor 22 is energized to drive unwinding reel R, relay A is energized and lifts its contact elements AI, A2, A3, A4, A5, A6 and A'l. When the leading end of the strip enters the rolls of the first roll stand L, a load is placed upon the roll motor I2 and this causes relay B to be actuated.

Since there is no front tension on the strip l0, as it is passed through the rolls of the iirst roll stand L, it is necessary that the back tension be higher than normal and of a predetermined amount in order that all portions of the strip I0 may receive substantially the same amount of reduction as it passes through the rolls of roll stand L. This predetermined higher-than-normal back tension is placed on the strip l0 by increasing the current ow in the shunt field winding 64 of motor 22. This increase in current in the shunt field winding 64 of motor 22 is eiected by the movement of contact element B6 of relay B to closed circuit position to close the circuit which functions to short circuit the resistance elements Gl and G2 and which comprises the conductor |42 leading from one side of the resistance element GI through the contact element C5, conductor |44, contact element B6 and conductor |46 to one side of the resistance element G2. At the same time, the regulator G is adjusted to maintain the higher-than-normal back tension on strip |0 by increasing the resistance in the coil of the operating solenoid 50 of regulator G. This is accomplished by the movementv of the contact element B1 of relay B to open circuit position. It will be seen that the movement of contact element B1 to open circuit position opens a circuit which has a shunt relation with the resistance elements G3 and G4 and which comprises one side of the resistance element G3, conductor |48, contact element B1 and conductor |50 to one side of the resistance element G4. The strip |0 thus has applied to it a higher-than-normal back tension while it is passing through the rolls of roll stand L and until its leading end enters the rolls of second lroll stand M.

As the leading end of strip |0 enters and `passes through the rolls of roll stand M, it will be seen that the only tension that can be applied to the strip |0 is back tension, and in order to secure the proper reduction in all parts of the strip I0, it is necessary that this back tension be higher-than-normal. The required higherthan-normal back tension is applied to the strip |0 by the tensioning device H by decreasing the energization of the coil of solenoid so as to increase the pressure on the strip |0 by increasing the pressure in the cylinder 16. This decrease in the energization of the coil of solenoid 90 is effected by the operation of relay C which is actuated when the increased load is placed on the roll motor I4 by the entry of the' leading end of the strip |0 between the rolls of the roll stand It will be seen that when relay C pis not actuated, a circuit which has a shunt relation to the resistance elements HI, H2 and H3 exists, and comprises conductor |52 from one side of resistance element H3, conductor |54, contact element C4 of relay C and conductor |56 to one side of resistance element HI. This higher-thannormal back tension will be maintained on the strip |0 by the tensioning device H which will automatically control the energization of the shunt field winding |08 of motor I4 and thus so regulate the torque of motor I4 as to maintain the desired tension of the strip I0.

With the higher-than-normal back tension maintained between the strip i0 and the rolls of the second roll stand M, it follows that the same higher-than-normal front tension will be applied between the strip l0 and the rolls of the rst roll stand L, and in order to maintain the uniform reduction of the strip I0 at the roll y stand L, it is necessary that the back tension between the strip l0 and the rolls of roll stand L as applied by the unwinding reel R be lowerthan-normal. This loWer-than-normal back tension between the strip |0 and the rolls of roll stand L is provided by decreasing the current ow in the shunt eld winding 64 of motor 22. This decrease in the current ow in shunt field Winding 54 is eiiected by connecting the resistance elements G| and G2 in series circuit relation with, the shunt field winding 64. The resistance elements GI and G2 are connected in circuit with the shunt eld winding 64 by opening the previously described shunting circuit comprising conductor |42, contact element C5. conductor |44, contact element B6 and conductor |46. It will be seen that this circuit is opened by the operation of relay C to move contact element C5 to open circuit position when the leading end of the strip enters the rolls of roll stand M. At the same time contact element C6' of relay 6 is moved to closed circuit position to close a shunting circuit for resistance elements G3 and G4 extending from one side of resistance element G3, conductors |48 and |10, contact element DB, conductor |12, contact element C6 and conductors |14 and |50 to resistance element G4. 'I'his shunting of resistance elements G3 and G4 decreases the resistance in the circuit of the coil of control relay 50 of regulatonGto decrease the back tension on the strip l0. Thus it will be seen that a higher-than-normal tension is maintained on the strip |0 between roll stands L and M and a lower-than-normal back tension is maintained at roll stand L while the leading end of the strip |0 is passing from the roll stand M to the roll stand N.

As the leading end of the strip |0 enters and passes through the rolls of the third roll stand N and until it enters the rolls of the last roll stand O, it is necessary that a higher-than-normal back tension be applied to the strip in order that a uniform reduction in all parts of thestrip 0 may be secured as the strip passes through the rolls of roll stand M.K This higher-than-nomal back tension is applied to strip |0 by increasing the resistance in the circuit of the regulating solenoid 90 of the tensioning device I to increase the pressure applied to the strip by the tensioning device I. This increase in the resistance in the circuit of the coil of regulating solenoid 98 is accomplished by opening a circuit which has a shunt relation to the resistance elements Il, I2 and I3 and which comprises conductor |58 from one side of resistance element I3, conductor |60, contact element D3 and conductor |62 to one side of the resistance element Il. This circuit is opened by the operation of relayD to move its contact element D3 to open circuit position when the leading end of the strip places a load upon the motor I6 as it enters the rolls oi roll stand M.

Inorder to prevent too great a reduction of the strip- I in the rolls of roll stand M, it is necessary that the back tension between the strip I8 and the rolls of roll stand M be decreased to lower-than-normal when the higher-than-normal front tension is established by the strip I0 and the rolls of roll stand M. This lower-thannormal back tension on the strip |0 is provided by connecting only resistance element H3 in cir-- cuit with the coil of the regulating solenoid 90 of the tensioning device H. It will be seen that when relay D operated, a circuit having a shunt relation with the resistance elements HI and H2 was established comprising conductor |64, contact element D4, conductor |66, contact element E3, and conductor |56 to one side of the resistance element H I.. With this adjustment of the energization of the coil of the regulating solenoid 90 of tensioning device H, a loWer-than-normal back tension will be maintained between the strip and the rolls of roll stand M and a lower-thannormal front tension will be maintained between the strip Ill and the rolls of the roll stand L.

In order to maintain the proper amount of tension on the strip I8 at the roll stand L, it is necessary that the back tension between the strip I0 and the rolls of roll stand L be increased to higher-than-normal at the time that the front tension between the strip and the rolls of roll stand L is decreased to lower-than-normal. This higher-than-normal back tension is produced by increasing the current iiow in shunt eld winding 64 of motor 22 by applying a shunting circuit to resistance elements GI and G2. This shunting circuit is completed bythe movement of the contact element D to the closed circuit position and comprises conductor |42 from one side of the resistance element GI, contact element E4, conductor |61, contact element D5, conductor |68, conductor |44, contact element B6 and conductor |46 to one side of resistance element G2. At the same time, the current in the coil of regulating solenoid 50 is decreased to cause the motor 22 to maintain the higher-than-normal back tension on the strip l0 by connecting resistance elements G3 and G4 in series circuit relation with the coil of solenoid 50. The resistance elements G3 and G4 are connected in circuit with the coil of solenoid 5D by the movement of the contact element D6 to open circuit position to open a shunting circuit for the resistance elements G3 and G4 which comprises one side of the resistance ele= ment G3, conductor |48, conductor |18, contact element D6, conductor |12, contact element C6, conductor |14, and conductor |50 to one side of the resistance element G4.

Thus it will be seen that while the leading end of the strip I0 passes from the roll stand N to the roll stand O, a higher-than-normal back tension will be maintained between the strip I0 and the rolls of roll stand N; a higher-than-normal front tension will be maintained between the strip ID and the rolls of roll stand M; a lowerthan-normal back tension will be maintained between the strip III and the rolls of roll stand M; a lower-than-normal front tension will be maintained between the strip Il) and the rolls of roll stand L, and a higher-than-normal back tension will be maintained between the strip ||l and the rolls of roll stand L, thus ensuring the proper reduction due to tensioning at each of these roll stands.

Throughout this description, the terms lowerthan-normal and higher-than-normal are used to designate tensions which when applied to the strip on opposite sides of the roll stand will produce a degree of reduction due to tension substantially equal to the reduction due to tension produced by normal tension on both sides of the roll stand. The lower-than-normal tension will be practically equal to no tension so far as its reducing effect on the strip is concerned. Where substantially constant total tensions are referred to 'in the specication and the claims the tensions which will produce constant reducing effects are meant. Constant total tensions at a roll stand are the tensions which will produce constant resulting reduction and may be either normal tension on both sides of the roll stand, higher-than-normal tension on one side of the roll stand with lower-than-normal tension on the other side or higher-than-normal tension on one side with no tension on the other side.

It is considered within the scope of this invention to provide fewer operationsfor correcting gauge than are described herein with each operation performing a greater degree of correction. It might be desirable, for instance, to provide increased tension between only two pairs of roll stands instead of between each pair of stands as herein described.

When the leading end of strip l0 enters the rolls of roll stand O and passes toward the reel S, it is necessary that a higher-than-normal back tension be applied between strip and the rolls of roll stand O, since it is not possible to apply a front tension between the strip and the rolls of roll stand O. This higher-than-normal back tension is applied and maintained by the tensioning device J when the contact element El is moved to the open circuit position by the operation of the relay E when the leading end of strip I0 places a load upon the motor I8 upon entering the rolls of roll stand O. The movement of contact element El to open circuit position removes a shunting circuit from the resistance elements J l, J2 and J3 which comprises one end of the resistance elements J3, conductor |16, conductor |18, contact element El and conductor to one side of the resistance element Jl. The tensioning device J automatically maintains this higher-than-normal tension between the strip I0 and the roll stands O and M while the leading end of the strip is moving from the roll stand O toward the winding reel S.

The application of higher-than-normal front tension between the strip I0 and the roll stand N makes it necessary that back tension between the strip I0 and the roll M be decreased to lowerthan-normal, so that the reduction of all parts of the strip at roll stand N may be uniform. The decrease in tension on the strip by the tensioning device I to lower-than-normal ls brought about by connecting only resistance element |3'in circuit with the coil of the regulating solenoid 90 of the tensioning device I. Resistance element I3 only is connected in circuit with the coil of solenoid 80 by applying ya shunting circuit to the'resistance elements I| and I2 which comprises one side oi' resistance element I2, conductor |82, contact element E2 'which was moved to closed circuit position by the operation of relay E when the leading end of the strip entered th'e` roll stand O, conductor |84, contact element F2, conductor |88 and conductor |82 to one side of the resistance element Il. Thus a lower than normal tension is applied to the strip I between roll stands N and M.

With lower-than-normal front tension between strip |0 and roll stand M, it is necessary that the higher-than-normai back tension be applied between the strip |0 and the roll stand M. This higher-than-normal back tension is applied to strip between the rolls and the roll stands M and L by again connecting resistance elements HI, H2 and H8 in series circuit relation with the coil of regulating solenoid 80 of the tension device H. This decreased deenergization of the coil of solenoid 90 is effected by removing the shunting circuit, hereinbefore described, for resistance elements H and H2 by the movement of contact element E3 to open circuit position upon the operation of relay E.

With the establishment of the higher-than- `normal front tension between the strip I0 and the roll stand L, it is necessary that the back tension between the strip l0 and the roll standl L be decreased to lower-than-nnrmal. This is accomplished by again connecting resistance elements G| and G2 in series circuit relation` with shunt iield winding 84 of motor 22 by removing the hereinbefore described shunting circuit for the resistance elements G| and G2 by the movement of the contact element E4 to open circuit position upon the operation of relay E. At the same time, the regulator G is adjusted for the lower-than-normal back tension by applying a shunting circuit to the resistance elements G8 and G4. This shunting circuit comprises conductor |50 from one side of the resistance element G4, conductor |14, contact element C8, conductor |12, conductor |88, contact element E5, conductor |80, contact element F8, conductor |10 and conductor |48 to one side of the resistance element G3. Thus it will be seen that the higher-than-normal tension will be maintained between the strip I0 and each of the roll stands as the leading end of thc strip moves from the roll stand O to the winding reel S.

After the leading end of the strip |0 has left the roll stand O and is started on the reel S, the load on the reel motor 20 will cause relay F to` operate and move contact element F8 to the open circuit position to remove a shunting circuit from the resistance elements Ki, K2, which comprises one side of resistance element K2, conductor 204, contact element F9 and conductor 208 to one side of the resistance element KI. With relay A energized a shunting circuit will be applied to the resistance element K2 which comprises one `side of resistance element K2, conductor 208, conductor 2|0, contact element A| and conductor 2|2 to the other side of resistance element K2. Thus resistance element KI will be connected in series circuit relation with the field winding |20 of motor 20 to cause the motor to apply a normal tension to the strip I8 as it is wound on reel S. 'I'he operation of relay F will move its contact element F8 to open circuit position to remove a shunting circuit from the resistance elements K8 and K4 which comprises conduc /r |92 from one side of the resistance elemen K3, conductor |94, contact element F8 and conductor |98 to one side of the resistance element K4. It will be seen that with relay A energized, the contact element A8 thereof will close a shunting circuit for resistance element K4 which comprises one side of resistance element K4, conductor |98,\contact element A6, conductor 200 and conductor 202 to the other side of the resistance element K4. This will leave such a resistance in circuit with the coil |22 of regulator K as to cause the regulator to maintain a normal front tension between the strip l0 and the roll stand O.

With normal front tension applied between strip |0 and roll stand O, it is necessary that normal back tension be applied between strip l0 and roll stand O in order to maintain the proper reduction due to tension at the roll stand O. This is done by applying a shunting circuit to resistance element JI and leaving resistance elements J2 and J8 connected in series circuit relation with the coil of regulating solenoid of tension device J. The shunting circuit for resistance J comprises conductor |80 extending from one side of resistance JI, contact element F| which was moved to closed circuit position when the leading end of the strip 0 started winding on reel S, conductor 2|4, contact element A3 and conductor 2|8 to the other side of resistance element Jl. With this adjustment of the circuit of the coil of thec regulating solenoid 80, the tensioning device J will maintain a normal tension onthe strip I0 between the roll stands O and M. It will be seen that this establishment of normal tension between adjacent roll stands and between the end roll stands and the reels will be necessary to maintain the proper tensions on the strip at each of the roll `stands. The establishment of the normal tensiorbetween roll stands N and M will be accomplished by connecting resistance elements I2 and Il in series circuit relation with the coil of the regulating solenoid of tensioning device I. This 90 for normal tension. This shunting circuit comprises conductor 224 extending from one side of the resistance element HI, contact element A5, conductor 228, contact element F4 and conductor |58 to the other side of the resistance element HI The establishment of normal back tension between strip |0 and roll stand L is accomplished by connecting only resistance element G2 in circuit with the field winding 84 of motor 22 to provide a normal back tension and connecting only the resistance element G4 in series circuit relation with the coil of the regulator solenoid 88 to maintain the normal back tension on the strip |0. Resistance element G2 only is connected in series circuit relationA with the iield winding 84 for establishing a shunting circuit for resistance GI which comprises one side of time, a shunting circuit is appned to the rethe resistance element GI, conductor |42, contact element F5 and conductor 228 to the other side of resistance element GI. Resistance elcment G4 only is connected in series circuit relationV with the coil of solenoid 50 for establishing a shunting circuit for resistance element G3 which comprises one side of resistance element G3, conductor |48, conductor |10, contact element F1 and conductor 230 to the other side of resistance element G3. Thus during the normal operation of the strip reducing mill, normal tensions will be applied to all parts of the strip.

When the following end of the strip leaves the reel R, there will be no back tension between the strip I and the roll stand L, and it is necessary to establish a higher-than-normal front tension between the strip |0 and the roll stand L so as to obtain the proper reduction of the part of the strip ||J between the roll stand L and the following end. To accomplish this, the tension applied to the strip I0 between the roll stands L and M by the tensioning device H is increased by decreasing the energization of the coil of regulating solenoid 90 of the tensioning device H. This decreased energization of the coil of solenoid 90 is accomplished by removing the shunting circuit for the resistance element HI, describedhereinbefore, by the opening of the contact element A5 due to the deenergization of the relay A when the following end of the strip l0 leaves the reel R.

With the establishment of the higher-thannormal back tension between the strip I0 and the roll stand M, it is necessary that the front tension between the strip l0 and the roll stand M be decreased to lower-than-normal. This is accomplished by applying a shunting circuit to the resistance elements Il and I2 of regulator I by the operation of relay A which closes its contact element A4 to close a circuit which comprises conductor 232, contact element A4, conductor 234, contact element B4 and conductor 236. Thus with only resistance element I3 connected in series circuit relation with the coil of solenoid 90, the tensioning device I will apply a lower-thannormal tension to the strip I0 between the roll stands M and N.

With the decrease in back tension between the strip |0 and the roll stand N, it is necessary that the front tension between the strip |0 and the roll stand N be increased to higher-than-normal. This is accomplished by connecting resistance elements JI, J2 and J3 in series circuit relation with the coil of operating solenoid 90 of the tension device J. Resistance elements J i, J2 and J3 are connected in this series circuit by the opening of the shunting circuit for the resistance element J hereinbefore described, due to the opening of contact element A3 of relay A. Thus a higherthan-normal tension will be applied to strip I0 between the roll stands N and O.

With the higher-than-normal back tension applied between strip |0 and roll stand O, it is necessary that a lower-than-normal front tension be applied between the strip |0 4and the roll stand O. The lower-than-normal tension between the strip l0 and roll stand O is established by increasing the current flow in the field winding |20 of winding reel motor 20 by shunting the resistance elements KI and K2 through a circuit which comprises one side of the resistance element K2, conductor 208, contact element A2, conductor 238, contact element Bl, conductor 240, contact element D2, and conductor 242 to one side of the resistance element KI. At the same sistance elements K3 and K4 to so adjust the current strength in the coil of regulator solenoid |22 as to maintain the lower-than-normal tension on the strip I0. A shunting circuit for the resistance elements K3 and K4 comprises one side of the resistance element K3, conductor |92, contact element D1, conductor 244, contact element B8, conductor 246, contact-element A1 and conductor 202 to one side of the resistance element K4. Thus it will be seen that the proper tensioning is maintained on the strip at each of the roll stands as the following end of the strip ls moving between the unwinding reel R. and the roll stand L.

The reel motor 22 may be stopped by operating the normally closed switch |33 to deenergize the holding circuit relay |32 which will, in turn, break the holding circuit of the circuit breaker |26.

When the following end of the strip I0 leaves the roll stand L, the decrease in the load on the roll motor |2 will permit the armature of relay B to drop. While the following end of strip |0 leaves the roll stand L and roll stand M, there can be no back tension applied between the strip |0 and the roll stand N. With the deenergization of relay B, it will be seen that contact element B3 will close a circuit having shunting relation with resistance elements HI, H2 and H3 which comprises one side of the resistance element HI, conductor 248, conductor 250, contact element B3, conductor 252 and conductor |52 to one side of the resistance element H3. This shunting out of the resistance from the circuit of the coil of the regulating solenoid 90 will permit such a current to flow in the coil of the solenoid 90 as will cause the constant pressure valve 18 to regulate the pressure in cylinder 16 to hold the idling roller 12 of tensioning device H in the idle position.

Since there is no back tension between the strip |0 and roll stand M after the end of the strip leaves roll stand L, it is necessary that the front tension between the strip |0 and the roll stand M be increased to higher-than-normal. This higher-than-normal tension is applied to' the strip between roll stands M and N by increasing the resistance in series with the coil of the regulating solenoid `90 to decrease the current flowin the coil. The resistance element I| is connected in series circuit relation with the coil of solenoid 90 by removing the hereinbefore described shunting circuit for resistance elements Il and I2 by the opening of contact element B4 of relay B.

The establishment of a higher-than-normal back tension between the strip |0 and the roll stand M makes it necessary that a lower-thannormal front tension between the strip 0 and the roll stand M be established. This is effected by the closing of the contact element B2 of relay B to close a shunting circuit for resistance elements J and J2 which comprises conductor 253 extending from one side of resistance element J2, contact element C2, conductor 254, contact element B2, conductor 256, conductor 2|4, contact element FI and conductor to one side of resistance element J|. With only resistance J3 in series circuit relation with the coil of regulating solenoid 90, it will be seen that a lower-thannormal tension will be applied by the tension device J to the strip |0 between the roll stands N and O.

The establishment of lower-than-normal back tension between the strip |0 and roll stand N makes it necessary that the front tension between the strip I and the roll stand O be increased to higher-than-normal. The higher-than-normal tension is applied to strip I0 by reel motor 20 by connecting resistance elements KI and K2 in series circuit relation with the eld winding |20 of motor 20 and connecting the resistance elements K3 and K4 in series circuit relation with the coil of the regulating solenoid |22. Both resistances KI and K2 are connected in series circuit relation with field winding |20 by the opening of contact element BI of relay B which opens the hereinbefore described shunting circuit for the resistance element K. Both resistances K3 and K4 are connected in series circuit relation with the coil of solenoid |22 by the opening of contact element B8 which breaks the hereinbefore described shunting circuit for resistances K3 and K4. 'Ihus it will be seen that While the following end of strip I0 is moving between roll stands L-and M higher-than-normal tension will be applied to the strip I0 between the roll stands M and N, lower-than-normal tension will be applied to the strip I0 between the roll stands M and O and higher-than-normal front tension will be applied to the strip I0 by the reel motor 20.

When the following end of the strip I0 leaves the roll stand M, the load will be removed from the roll motor I4 and the 'armature of relay C will be permitted to drop. With the contact element C3 in closed circuit position, a shunting `circuit comprising conductor 258, contact element C3, conductor 260 and conductor 236 will be applied to the resistance elements II, I2 and I3 to so increase the current flow in the coil of the regulating solenoid 90 so as to cause the roller of the tensioning device I to be held in idling position.

With no back tension between the strip I0 and the roll stand N, it is necessary that the tension on the strip I0 betweenroll stands N and O be increased to higher-than-normaL This higherthan-normal tension is obtained by the opening of the contact element C2 of relay C to break the hereinbefore described shunting circuit from resistance elements J and J2. 'I'his willV cause resistance elements J I, J2 and J3 to be connected in series circuit relation with the coil of the regulating solenoid 90, thus causing tensioning device J to maintain a higher-than-normal tension on the strip I0.

With higher-than-normal back tension between the strip I0 and roll stand O', the front tensioning of strip I0 by reel motor 20 is decreased to lowerthan-normal by the closing of contact element CI of relay C to complete a shunting circuit for the resistance elements vKl and K2 which comprises one side of resistance element K2, conductor 208, contact element CI, conductor 262, conductor 240, contact e1ement'D2 and conductor '242 to one side of the resistance element KI. At

the same time ashunting circuit is applied to resistance elements K3 and K4 which comprises one side of the resistance element K3, conductor |92, contact element D1, conductor 244, contact element C1 and conductor 202" to one side of the resistance element K4. This shunting of the resistance elements KI and K2 and K3 and K4 establishes such current values in the field coil |20 of motor 20 and the coil of regulating solenoid |22 as to cause motor 20 to maintain a lower-than-normal tension on the strip I0.

As the following end of the strip I0 passes through the rolls of roll stand N, the roll motor I6 is relieved of its load and the relay D is permitted to drop its armature.

contact element DI to closed circuit position l completes a shunting circuit for the resistance elements J I, J2 and J3 of regulator J comprising conductors |16, 264, contact element DI, conductor 266, and conductor 268 to thus cause tensioning device J to hold its tensioning roller in the idling position. Since there is no back tension applied between strip I0 and the roll stand O while the following end oi' strip I0 is moving from roll stand N to roll stand O, higher-thannormal tension is applied to the strip I 0 by the reel motor 20. To cause motor |20 to apply and maintain this higher-than-normal tension to the strip I0, resistance elements KI and K2 and K3 and K4 are connected in series circuit relation withthe coil of solenoid |22 and the Iield winding |20 of motor 20, respectively. Resistance elements KI and K2 are connected in series circuit relation with the field winding |20 by the opening of contact element D2 which breaks the hereinbefore described shunting circuit for the resistance elements KI and K2. The resistance elements K3 and K4 are connected in series circuit relation with the winding of the relay |22 by the opening of contact element D1l to break the hereinbefore described shunting circuit for the resistance elements K3 and K4. Thus a higher-than-normal front tension will be applied between the strip I0 and roll stand O while the following endv of the strip I0 is travelling from the roll stand N to the roll stand O.

It is understood that the normal lower-thannormal and higher-than-normal tensions referred to hereinbefore may have different values at the different tension applying points, since to secure the proper reduction of the strip, the tensions applied to the strip may have to be of different values as the strip progresses through the mill from stand to stand and is progressively reduced in thickness. These diierent values of tensioning may be secured and the desired predetermined tensions provided by properly selecting the values of the adjustable resistance elements GI, G2, G3, G4, 296 and 298, associated with reel motor 22, HI, H2, H3 and 300, associated with the tensioning device H, II, I2, I3 and 302, associated with tensioning device I, J I, J2, J3 and 304, associated with tensioning device J, and KI, K2, K3, K4, 2'84 and 306 associated with reel motor 20.

When the following end of the strip I0 passes through the rolls of roll vstand O, the load on the roll motor I8, will be decreased sufciently to permit the armature of relay E to drop. The opening of contact element E6 of relay E will break the holding circuit for the coil of circuit breaker |34 which extends from the positive side of the source of power as shown through conductor 210, the operating coil of circuit breaker |34, conductor 212, conductor 214, contact element I4|, conductor 216, conductor 218, contact element'ES and conductors 280 and 282 to the negative side of the source of power as shown. 'I'he deenevrgization of the operating coil of the circuit breaker |34 will permit the circuit breaker to open to deenergize the winding reel motor 20.

The movement of The winding reel motor the manually controlled the Winding of the strip IIl'on the reel S.

The adjustable resistances 284, 286, 288, 230, 294 and 296 are connected in series circuit relation with the shunt field windings of the motors 20, I8, |6,'| 4, I2 and 22, respectively, so that manual `adjustments for the proper operating conditions mail be made. Likewise. variable remay then be inched by switch |26 to completesistances 288, 300, 302, 304 and 306 are connected in series circuit relation with the regulating solenoidsof the regulator G, the tensioning devices H, I and J and the regulator K, respectively, so that each of these regulators may be adjusted manually for the proper operating condtions.

When such a strip rolling system as hereinbefore described is used to roll hot strip, the strip gradually cools as it is fed through the mill and as its temperature decreases, its resistance to rolling increases, and, as a result, the thickness of the finished product gradually increases from the leading to the following end of the strip. In order to produce uniform thickness of the strip throughout the entire length of the strip, temperature responsive devices have been provided fer varying the tensions applied to the strip as it passes through the mill, so that reducing tensions may be increased as the strip cools to compensate for the resistance to reduction of the strip due to the decrease in its temperature. These temperatureV responsive devices comprise thermostat elements 308 and 3|0 mechanically connected to rheostats 3|2 and 3|4, respectively. The rheostat 3|2 is connected in parallel circuit relation with resistance element 3|6 in the circuit of field winding 64 of motor 22 so as to increase the current flow therein and thereby increase the back tension in proportion to the decrease in temperature of the strip l0. While at the present time tension is not commonly applied,to the strip at the feed and delivery ends of the mill in a hot strip mill, this invention includes means for so operating the hot strip mill and it is within the scope of this invention to omit the tensioning at these points if it is so desired.

The rheostat 3l4 is connected in parallel circuit relation with resistance element 3|8 in the circuit of field winding |20 of motor 20 so as to decrease the current flow therein in accordance with the decrease in temperature 'of the strip I to thus cause motor 20 to increase the tension on the strip I0. Y

Thermostat elements 320, 322 and 324 are connected to operate rheostats 326, 328 and 330, respectively, and are so connected in the circuit of the coils of the regulating solenoids 90 of the tensioning devices H, I and J, respectively, as to decrease the current flow in the coils of solenoid 90 with the decrease in temperature of the strip I0 to thus cause the tensioning devices H, I and J to increase the tension on the strip I0 in proportion to the decrease in temperature thereof. It is within the scope of this invention to use a smaller number of temperature responsive devices and adjust for temperature change on fewer tensioning devices if suchV operation is found more practicable.

Since the thickness of the strip as it is fed to the mill may vary, and therefore, require the application ol variable reducing forces to produce the desired reduction in the mill and, since it is desired that the finished product have as near a uniform predetermined thickness as is possible, means res'pensive to the thickness of the strip at various stations along the strip are provided, for

4varying the tension on the strip at the various tensioning points so that the reducing forces may be so varied as to produce a finished strip of substantially uniform thickness. These thickness responsive devices may be of any well known construction.

The thickness responsive device 332 comprises a pair of conducting roller elements 334 biased to bear upon the strip I0. A resistance responsive device 336 which may be the usual Wheatstone bridge arrangement or any other electrical equipment responsive to the resistance of the strip between the rollers 334, is connected to rollers 334 and is caused to operate the rheostat 338. The rheostat 338 is connected in parallel circuit relation with the resistance element 340 which, in turn, is connected in series circuit relation with the eld winding |20 of reel motor 20.

Variations in the thickness of the strip l0 at the point where the strip is engaged by conducting rollers 334 will cause the resistance responsive device 336 to vary the adjustment of the rheostat 338 to thus affect the field current of reel motor 2'0 to causethe motor 20 to vary the tension on the strip I0.

In like manner, a thickness responsive device 342 is utilized to vary the iield current of unwinding reel machine 22 to vary the tension on strip I0 between the unwinding reel and the roll stand L. The thickness responsive devices 344, 346 and 348 likewise function to vary the current ow through the regulating solenoids of the tensioning devices H, I, and J in response to variations in the thickness of the strip. Each of these thickness devices is so calibrated as to cause a change in the strip tension in response to any variation of the thickness of the strip from the predetermined desired thickness at th'e point where the thickness responsive device is located. It is understood that a smaller number of thickness ,responsive devices may be used for correcting gauge at any desired number of tensioning points.

In Fig. 4 there is shown a modification of the invention in which the draft taken by the rolls of the mill is varied in accordance with variations in thickness and temperature of the strip to thus vary the reducing effort with variations in strip thickness and strip temperature. be apparent that as the thickness of the strip increases the reducing effort must be increased to produce a given resultant strip thickness. Similarly as the temperature of the strip decreases, as it will when hot strip is being rolled, the resistance to reduction will increase and necessitate an increased reducing effort in order to produce a given resultant strip thickness. In the embodiment of the invention discussed hereinbefore in connection with Figs. 1, 2 and 3 of the drawings, the variations in reducing effort necessitated by changes in strip thickness and temperature are provided by an automatic screw down controlled by thickness and temperature responsive devices.

Referring to Fig. 4, a screw down device 350 is arranged to be driven by motor 352 to decrease or increase the spacing between the rolls and to thus vary the draft taken by the rolls. 'I'he contact elements 354 and 356 are the contact elements of reversing switch 355 and are biased in the upper closed circuit position by spring member 358 and are disposed to be actuated by the core of solenoid 360. A strip thickness responsive device 362, which may be any such device commonly used for determining material thickness, but which is shownas essentially the same as the thickness responsive devices 332, 342, 344, 346 and 348 discussed hereinbefore in connection with the system shown in Figs. 1, 2, 3, is provided for -varying the energization of the solenoid 360 `in accordance with variations in the thickness of the strip I 0. A

It will thermal responsive device 364 is sopositioned as to be responsive to temperature changes in the strip I6. A resistance element 366 is connected in series circuit relation with the coil of solenoid 360 and a rheostat 368 is connected in shunt circuit with it. The rheostat368 is disposed to be actuated by temperature responsive device 364 so that variations in the temperature of the strip I will cause variations in the current flow in the coil of solenoid 360.

In the operation of the system, the thickness and temperature responsive devices 362 and 364 are so adjusted as to cause such current ow in the coil of solenoid 360 of switch 355 as will keep the contact elements 354 and 356 in the Dosition shown in the drawings which is between the upper and lower closed circuit positions. If the thickness of the strip should change for any reason the thickness responsive device 362 will cause such ,a change in the current flow in the coil of solenoid 360 as will effect closure of the reversing switch contact elements to energize the motor 352 so as to cause the motor to operate the screw down device 350 in the necessary direction to correct the condition. The thickness responsive device will then respond to the changed thickness and return the reversing switch 355 to/its neutral position.

When the mill is rolling hot strip and the strip cools, the temperature responsive device 364 will function to change the resistance characteristie of the solenoid circuit. As a result the motor 352 will be energized to actuate the screwdown device in such a direction as to increase the draft taken by the rolls of roll stand L.

The apparatus of Fig. 4 differs from that of Fig. 3 only in the substitution of screw down control in Fig. 4, for tension control in Fig. 3 in response to thickness and temperature. 'I 'he apparatus of Fig. 4 is interchangeable with that of Fig. 3 and accordingly the same reference characters have been applied to the like elements and circuits. It is to be understood that the thickness and temperature responsive screw down system of Fig. 4 may be applied to any or all of the roll stands of the system shown in Figs. 1, 2 and 3. It is further to be understood that the system may be made to operateA in accordance with the principles described herein so that both the draft and the tension on the strip may be varied in response to changes in strip thick-- ness and temperature.

It is also to be understood that tensioning devises other than thefparticular ones shown and described may be used. that thermostat elements other than the ones shown and described may be used, and forward and back tension regulating devices for the reel motors other than those shown and described and any other equivalent devices may be used to accomplish the desired results without the exercise of invention.

It will be seen that I have provided a control system for a strip rolling mill which is reliable and eflicient in operation, and which will so control the reducing forces on a strip of material as it is fed through the mill as to produce a strip of uniform thickness throughout the length of the strip.

In compliance with the requirements of the patent statutes, I have shown and described herein the preferred embodiment of my invention. It is understood, however, that the invention is not limited to the precise construction shown and described, but is capable of modification by one skilled in the art, the embodiments herein shown being merely illustrative of the principles of my invention.

I claim as my invention:

1. In a strip rolling mill, a set of cooperating rolls, an unwinding reel and a winding reel for the strip material, means including said unwinding reel for applying back tension to the strip as it passes between said rolls, means including said winding reel for applying front tension to the strip as it passes between the rolls,

'means for causing said back tensioning means to apply an abnormal tension to the strip from the time at which the leading end of the strip enters the rolls until said leading end is attached to and tensioned by the winding reel, means for causing said front tensioning means to apply an abnormal tension to the strip from the time the following end of the strip leaves the unwinding reel until said following end passes through said rolls, and means Ior causing said front and back tensioning means to apply normal tensions to the strip While the strip is being simultaneously unwound from one reel and wound upon the other reel.

2. In a strip rolling mill having a winding reel for the strip material, means including said winding reel for applying front tension to the strip as the strip passes through the mill, and means for applying an abnormal back tension to the strip from the time the leading end of the strip enters the rolls until said end of the strip is 1 started Winding on said winding reel.

3. In a strip tensioning control system for a multi-stand rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the strip with respect to the roll stands and winding and unwinding reels for establishing substantially constant total tensions on the strip at each roll stand while the strip is passing therethrough throughout substantially the entire length of the strip as it passes through the mill, yand means responsive to the temperature of the strip and the thickness of the strip for varying the total tensions on the strip at the roll stands.

4. In a strip rolling mill, a winding reel and an unwinding reel for the strip material, means including said winding reel for applying front tension to the strip as it passes through the rolls, means including said unwinding reel for applying back tension to the strip as it passes through the rolls, and means for causing said back tensioning means to apply an abnormal tension on the strip while the leading end of the strip is passing from the rolls to winding position on the winding reel.

5. In a strip rolling mill, a winding reel and an unwinding reel for strip material, means including said winding reel for applying front tension to the strip as it passes through the mill, means including said unwinding reel for applying back tension to the strip as it passes through the rolls, 'and means for causing said front tensioning means to apply an abnormal tension on the strip while the following end of the strip is passing from the unwinding reel to and through the rolls.

6. In a strip rolling mill, a winding reel and an unwinding reel for the strip material, means including said Winding reel for applying front tension to the strip as it passes through the rolls, means including said unwinding reel for applying back tension to the strip as it passes through the rolls, means for'causing said back tensioning means to apply an abnormal tension on-the strip while the leading end of the strip is passing from sion to the strip as it passes through the rolls,

means including said unwinding reel for applying back tension to the strip as it passes through the rolls, means for causing said front tensioning means to apply an abnormal tension on the strip while the following end of the strip is passing from the unwinding reel to and through the rolls` and means for causing both of said tensioning Cil means to apply normal tensions to the strip while I the strip is being both wound and unwound simultaneously.

8. In a strip rolling mill, means for applying back tension to the strip as it'passes through the rolls, means for applying front tension to the strip as it. passes through the rolls, and means for causing said back tensioning means to apply an abnormal tension to the strip from the time the leading end of the strip enters the rolls untilfront tension is applied to the strip by the front tensioning means. Y

9. In a strip rolling mill, means for applying back tension to the strip as it passes through the back tensionis taken from the strip until the end.

of the strip passes through the rolls.

10. In a strip rolling mill, means for applying back tension to the strip as it passes through the rolls, means for applying front tension to the s :ip las it passes through the rolls, means for causing said back tensioning means to apply an abnormal tension to the strip from the time the leading end of the strip enters the rolls until front tension is applied to the strip by the front tensioning means, and means for causing both of said tensioning means to apply normal tensions to the strip after front tension is applied to the strip.

11. In a strip rolling mill, means for applying back tension to the strip as it passes through the rolls, means for applying front tension to the strip asit passes through the rolls, means for causing said front tensioning means to apply abnormal tension 'to the strip from the time the back tension is taken from the strip until the end of the strip passes through the rolls, and means for causing both of said tensioning means to apply normal tensionstothe strip while both front and back tensions are applied to the strip simultaneously. Y j

12. In a strip tensioning control system for a multi-stand rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the strip with respect to the roll stands and winding and unwinding reels for establishing substantially constant total tensions on the strip at each roll stand while the strip is passing therethrough throughout substantially the entire length of the strip as it passes through the mill, and means responsive to the thickness of the stripfor varying the total tensions on the strip at one or more of the roll stands.

13. In a strip tensioning control system for a multi-stand strip rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the .strip with respect to the rollstands and winding and unwinding reels for establishing substantially constant total reducing tensions on the strip at each roll stand While the strip is passing therethrough throughout the entire length of the strip as it passes through the mill, and means responsive to variations in the thickness of the strip for varying the screw down adjustment of the mill rolls.

14. In a strip tensioning control system for a multi-stand strip rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the strip with respect to the roll stands and winding `and unwnding reels for establishing substantially constant total reducing tensions on the strip at each roll stand while the strip is passing therethrough throughout the entire length of the strip as it passes through vthe mill, and means responsive to variations in the temperature of the strip for varying the screw down adjustment of the mill rolls.

15. In ,a tensioning devicev for a multi-stand y strip rolling mill, a winding reel and an unwinding reel for the strip of material, means for producing abnormal tensions in the strip on one side of each of the roll stands and subnormal tensions in the strip on the opposite side of each of the roll stands as the leading end of the strip of material passes from the rst roll stand to winding engagement with the winding reel and as the following endof the strip of material passes from the unwinding reel through the last roll stand, and means for maintaining normal tensions on the strip on each side of each roll stand while the leading and following ends of .the strip are on the lil) winding and unwinding reels.

`strip rolling mill having winding and unwinding reels, tensioning means bearingon the strip between adjacent roll stands and acting upon the reel motors for applying adjustable tensionsto` the strip between the roll stands and between the end roll stands and the adjacent reels, means for adjusting said tensioning means to apply normal tensions to all parts of the strip while both the leading and following ends of the strip are wound on the said reels, means responsive to the positioning of the leading end of the strip for adjusting said tensioning means to apply abnormal tension to the strip between the pair of roll stands which is engaging the strip immediately adjacent the leading end of the strip and between alternate pairs'of roll stands engagingthe strip while applying subnormal tension between intervening -pairs of roll stands and applying an abnormal backtension on the strip between the unwinding reel and the first stand when the front tension on the strip at the rst stand is subnormal, and a subnormal back tension on the strip between the unwinding reel and the first stand when the front tension on the strip at therst stand is abnormal, while the leading end of the strip is being threaded through the mill from the first rollI stand to winding relation with the winding ree 17. In a, tensioning system for a multi-stand strip rolling mill having motor-operated winding and unwinding reels, tensioning means bearing on the strip between adjacent 'roll stands and controlling the reel motors for applying adjustable tensions to the strip between adjacent roll standsV and between the end roll stands and the adjacent reels, means for adjusting said tension- 16. In a tensioningsystem for a multi-stand ing means to apply normal tensions to all parts of the strip as it passes through the rolls while both the leading and the following ends of the strip are wound on their respective reels, means responsive to the positioning of the following end of the strip for adjusting said tensioning :means to apply abnormal tension to the strip between the pair of roll stands which is engaging the strip immediately adjacent the following end of the strip and between alternate pairs of roll stands engaging the strip While applying subnormal tension between intervening pairs of roll stands and applying subnormal tension on the strip between the winding reel and the last roll stand when the back tension on the strip at the last roll stand is abnormal and abnormal tension on the strip between the winding reel and the last roll stand when the back tension on the strip at the last -roll stand is subnormal, while the following end of the strip is passing from the unwinding reel to and through the last roll stand.

18. In a tension control system for a strip rolling mill having winding and unwinding reels and first, second, third and fourth roll stands, individually adjustable tensioning means bearing on the strip between each adjacent pair of roll stands, adjustable tensioning means for applying a back tension on the strip between the unwinding reel and the first roll stand, adjustable tensioning means for applying a front tension on the strip between the winding reel and the last roll stand, means responsive to the entry of the leading end of the strip into the flrst roll stand for causing said back tensioning means to establish an abnormal back tension on the strip; means responsive to the entry of the leading end of the strip into the second roll stand for causing said tensioning means between the first and second roll vstands to establish an abnormal tension on the strip between the first and second roll stands and for causing said back tensioning means to establish a subnormal back tension on the strip at the first roll stand; means responsive to .the entry of the leading end of the strip into the third roll stand for causing said tensioning means between the second and third roll stands to establish an abnormal tension on the strip between the second and third roll stands, for causing said tensioning means between the rst and second stands to establish a subnormal tension on the strip between the rst and second roll stands and for causing said back tensioning means to establish an abnormal back tension at the first roll stand; means responsive to the entry of the leading end of the strip into the fourth roll stand for causing said tensioning means between the third and fourth roll stands to establ lish an abnormal tension on the .strip between the third and fourth roll stands, for causing the tensioning means between the second and third roll stands to establish a subnormal tension on the strip between the second and third roll stands, for causing the tensioning means between the first and second roll stands to establish an abnormal tension on the strip between the first and second roll stands, and for causing said back tensioning means to establish a subnormal back tension on the strip at the rst roll stand; means responsive to the establishment of winding relation between the strip and the winding reel for causing said front tensioningmeans to establish a normal front tension on the strip at the fourth roll stand, for causing the tensioning means between the rst and second roll stands, the second and third roll stands and the third and fourth roll stands to establish normal tension on the strip between said pairs of stands, and for causing said back tensioning means to establish a normal back tension on the strip at the first roll stand; means responsive to the complete unwinding of the strip from said unwinding reel for causing the tensioning means between the first and second roll stands to establish an abnormal tension on the strip, for causing the tensioning means between the second and third roll stands to establish a subnormal tension on the strip, for causing the tensioning means between the third and fourth roll stand to establish an abnormal tension on the strip, and for causing said front tensioning means to establisha subnormal tension on the strip; means responsive to the passing of the following end of the strip through the' first roll stand for causing the tensioning means between thesecond and third roll stands to establish an abnormal tension on the strip, for causing the tensioning means between the third and fourth roll stands to establish a subnormal tension on the strip, kand for causing the front tensioning means to establish an abe normal front tension on the strip at the fourth roll stand; means responsive to the passing of the following end of the strip through the second roll stand for causing the tensioning means between the third and fourth roll stands to establish an abnormal tension on the strip, and for causing the front tensioning means to establish a subnormal front tension on the strip at the last roll stand; means responsive to the passing of the following end of the strip through the third roll stand for causing the front tensioning means to establish an abnormal front tension on the strip at the last roll stand, and means cooperating with the several tensioning means for maintaining the established tensions.

19. In a strip tensioning control system for a multi-stand metal strip rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the strip with respect to the roll stands and winding and unwinding reels for establishing substantially constant total tensions on the strip at each roll stand while the strip is passing therethrough throughout the entire length of the strip as it passes through the mill, and means responsive to variations in the temperature of the strip for varying the total tensions on the strip at the roll stands.

20. In a strip tensioning control system for a multi-stand metal strip rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the strip with respect 'to the roll stands and winding and unwinding reels for establishing and maintaining substantially constant reductiondue-to-tension effects on the strip at each roll stand while the strip is passing therethrough throughout the entire length of the strip as it passes through the mill.

21. In a strip tensioning control system for a multi-stand metal strip rolling mill having winding and unwinding reels, means responsive to the I positions of the leading and following ends of the strip with respect to the roll stands and winding and unwinding reels for establishing and maintaining substantially constant reductiondue-to-tension effects on the strip at each roll stand While the strip is passing therethrough throughout the entire length of the strip as it passes through the mill, and means responsive to variations in the temperature of the strip for varying the reduction-due-to-tension en'ects on the strip. i

22. In a strip tensioning control system for a multi-stand metal strip rolling mill having winding and unwinding reels, means responsive to the positions of the leading and following ends of the strip with respect to the roll stands and winding and unwinding reels for establishing and maintaining substantially constant reductiondue-to-tension effects on the strip at each roll stand while the strip is passing therethrough throughout the entire length oi the strip as it passes through the mill, and means responsive to the temperature of the strip and the thickness of the strip for varying the reduction-due-totension eilects on the strip.

23. In a strip tensioning control system for a multi-stand metal strip rolling mill having winding and unwinding reels, means vresponsive to the positions of the leading and following ends of the strip with respect to the roll stands and winding and unwinding reels for establishing and maintaining substantially constant reduction-due-to-tension eiects on the strip at each roll stand while the strip is passing therethrough throughout the entire length of the strip as it passes through the mill, and means responsive to the thickness oi' the strip for varying the reduction-due-to-tension effects on the strip.

24. A control system for material modifying apparatus and the like having a pair of elements operating successively on a length of material and individual dynamo-electric machines mechanically coupled to said elements comprising in combination, a current regulator for maintainingthe armature current o! one of said machines substantially constant, and means responsive to variations in the thickness of said material for controlling the other of said dynamo-electric machines to vary the tension of said materal to decrease the thickness variations of said material.

25. A control system for rolling mill apparatus and the like havingV a plurality of elements for successively operating on a length of moving material, and an electricv motor for driving one of said elements and a second electric motor i'or driving another 0f said elements comprising in combination, a current regulator for maintaining the currentJ input to one of said motors substantially constant, and means responsive to variations in the thickness of said material for controlling the speed ot the other of said motors to vary the tension of said material to decrease the thickness variations oi said material.

GLENN E. STOLTZ. 

